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| United States Patent |
5,274,019
|
|
Poyner
, et al.
|
December 28, 1993
|
Photodegradable compositions
Abstract
A polymer composition comprises a minor amount of a pro-degradant selected
from essentially carboxycylic .beta.-diketones and metal complexes
thereof, e.g. 2,2'-methylene(1,3-cyclohexanedione) or its Mn(II) or Zn
complex. A film of the composition may be used for the protection of seeds
or seedlings at an agricultural or horticultural locus.
| Inventors:
|
Poyner; William R. (Worcestershire, GB2);
Chakraborty; Khirud B. (Birmingham, GB2)
|
| Assignee:
|
Robinson Brothers Limited (West Bromwich, GB2)
|
| Appl. No.:
|
049516 |
| Filed:
|
April 19, 1993 |
Foreign Application Priority Data
| Current U.S. Class: |
524/358; 523/124; 523/125 |
| Intern'l Class: |
C08J 005/08 |
| Field of Search: |
523/124,125
524/358
|
References Cited
U.S. Patent Documents
| 3852227 | Dec., 1974 | Matsoda et al. | 524/358.
|
| 4056665 | Nov., 1977 | Taylor et al. | 524/358.
|
| 4102839 | Jul., 1978 | Crochemore et al. | 524/358.
|
| 4121025 | Oct., 1978 | Scott et al. | 523/125.
|
| 4252698 | Feb., 1981 | Ito et al. | 260/18.
|
| 4360606 | Nov., 1982 | Tobias et al. | 523/125.
|
| 4939194 | Jul., 1990 | Scott et al. | 523/126.
|
| 5070128 | Dec., 1991 | Gay | 524/357.
|
| Foreign Patent Documents |
| 391811 | Oct., 1990 | EP.
| |
| 2423510 | Nov., 1979 | FR.
| |
Other References
Yogev, A., Studies in Linear Dichroism, Journal of the American Chemical
Society, vol. 74, No. 6, 6059-6061, Oct. 7, 1970.
|
Primary Examiner: Schofer; Joseph L.
Assistant Examiner: Mulcahy; Peter D.
Attorney, Agent or Firm: Parmelee, Bollinger & Bramblett
Parent Case Text
This is a continuation of copending application(s) Ser. No. 07/782,405, on
Oct. 25, 1991"now abandoned.
Claims
What is claimed is:
1. A polymer composition comprising a polyolefin polymer and a
pro-degradant effective amount of a pro-degradant selected from
essentially carboxyclic .beta.-diketones and metal complexes thereof of
the formula
##STR2##
wherein n is 0, 1, 2 or 3; R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are
independently selected from H, a hydrocarboyl radical or a substituted
hydrocarbyl radical of up to 18 C atoms, any substituents using chosen
from oxo(.dbd.C), Nh.sub.2, (di)hydrocarboylamino, acylamino, COOH,
hydrocarbyloxycarbonyl, CN, halogen and NO.sub.2, or two of R.sup.1,
R.sup.2 and R.sup.3, together with the Catoms to which they are attached,
form an aromatic ring optionally substituted as defined above, Z is a
metal and m is an integer equal to the valence of Z; or (CR.sup.3
R.sup.4).sub.n is replaced by a heteroatom.
2. A polymer composition comprising:
(1) a polyolefin polymer,
(2) one or more additives selected from metal di(C.sub.5-20
alkyl)dithiocarbamates and thiuram sulfides, and
(3) a pro-degradent effective amount of a pro-degradant selected from
essentially carboxycylic .beta.-diketones and metal complexes thereof of
the formula
##STR3##
wherein n is 0, 1, 2 or 3; R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are
independently selected from H, a hydrocarbyl radical or a substituted
hydrocarbyl radical of up to 18 C atoms, any substituents being chosen
from oxo(.dbd.O), NH.sub.2, (di)hydrocarbylamino, acylamino, COOH,
hydrocarbyloxycarbonyl, CN, halogen and NO.sub.2, or two of R.sup.1,
R.sup.2 and R.sup.3, together with the C atoms to which they are attached,
form an aromatic ring optionally substituted as defined above; and
either m is 1 and 2 is H, a metal, a hydrocarbyl radical or a substituted
hydrocarbyl radical as defined above, or m is an integer other than 1 and
Z is a metal, a hydrocarbyl radical or a substituted hydrocarbyl radical
as defined above, having the valency m; or (CH.sup.3 R.sup.4).sub.n is
replaced by a heteratom.
3. A film of a composition comprising:
(1) a polyolefin polymer,
(2) an antioxidant amount of phenolic and antioxidant,
(3) from about 0.01 to about 5% by weight of a pro-degradant, and
(4) optionally one or more additives selected from metal di(C.sub.5-20
alkyl)dithiocarbonates and thiuram sulfides,
wherein the pro-degradant has the formula
##STR4##
wherein n is 0, 1, 2 or 3; R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are
independently selected from H, a hydrocarbyl radical or a substituted
hydrocarbyl or up to 18 C atoms, any substituents being chosen from
oxo(.dbd.0), NH.sub.2, (di)hydrocarbylamino, acylamino, COOH,
hydrocarbyloxycarbonyl, CN, halogen and NO.sub.2, or two of R.sup.1,
R.sup.2 and R.sup.3, together with the C atoms to which they are attached,
form an aromatic ring optionally substituted as defindd above; and m is 2
and Z is --CHR-- and R is H a hydrocarbyl radical or a substituted
hydrocarbyl radical as defindd above; or (CR.sup.3 R.sup.4).sub.n is
replaced by a heteroatom.
4. A compositions according to claim 1, wherein the polyolefin polymer is
selected from polypropylene and polyethylene.
5. A composition according to claim 1, which additionally comprises a metal
di(C.sub.5-20 alkyl)dithiocarbamate.
6. A composition according to claim 1, wherein the dithiocarbonate is zinc
diisononyldithiocarbamate.
7. A composition according to claim 1, which additionally comprises a
thiuram sulfide.
8. A composition according to claim 7, wherein the sulfide is
tetrabenzylthiuram disulfide.
9. A compositions according to claim 1, which comprises 0.01 to 5% by wt of
the pro-degradant, with respect to the polymer.
10. A compositions according to claim 2, wherein m is 2 and Z --CHR--, R is
H, a hydrocarbyl radical or a substituted hydrocarbyl radical.
11. A composition according to claim 2, wherein the prodegradant is
selected from 2,2'-methylenebis(1,3cyclohexanedione) and
2,2'-benzylidenebis(1,3cyclohexanedione).
12. A composition according to claim 2, which additionally comprises a
metal di(C.sub.5-20 alkyl)dithiocarbamate.
13. A composition according to claim 2, wherein the dithiocarbamate is zinc
diisononyldithiocarbamate.
14. A composition according to claim 2, which comprises 0.01 to 5% by wt of
the pro-degradant, with respect to the polymer.
15. A composition according to claim 3, which additionally comprises a
metal di(C.sub.5-20 alkyl)dithiocarbamate.
16. A composition according to claim 3, wherein the dithiocarbamate is zinc
diisononyldithiocarbamate.
17. A composition according to claim 11, which comprises 0.01 to 5% by wt
of the pro-degradant, with respect to the polymer.
Description
FIELD OF THE INVENTION
This invention relates to polymer compositions having controlled or
deliberately shortened lifetimes.
BACKGROUND OF THE INVENTION
Photodegradable compositions are useful, for example, for making
agricultural mulching film which can be used to protect seeds and
seedlings but which rapidly degrades so that it does not interfere with
ripening, harvesting or replanting. Such compositions are also useful to
prevent the accumulation of litter.
It is well known that polymeric materials, especially plastics, are
degraded by the action of heat, light and air. Apart from polymers
specifically designed for high temperature applications, most polymers
undergo heat degradation only during melt processing and forming. Usually,
however, polymers are subject to light and air throughout their life, and
the length of their life can be controlled by a suitable choice of
additives.
Various systems have been suggested for controlling the life of polymers.
For example, polymers have limited life if carbonyl groups are
incorporated into the polymer by copolymerisation or graft
copolymerisation. This technique has the disadvantage that separate
polymerisations have to be carried out to produce polymers with different
lifetimes. Consequently, it is often preferable to add pro-degradants to a
polymer during processing.
Pro-degradants or pro-oxidants are usually compounds of multi-valent
metals. U.S. Pat. No. 3,454,510 discloses as pro-oxidants the
acetylacetonates of Mn, Co, Cr, Fe, Cu or V, the C.sub.8-18 alkyl
acetoacetate or C.sub.8-18 alkylbenzoylacetate complexes of the same
metals, Zn or Ni, or the stearates or oleates of Mn(II) and Co(II).
Addition of one or more of these compounds to a polymer enables films to
be prepared which last only during the growing period of a crop.
U.S. Pat. No. 4,048,410 discloses the addition to polymers of organic
chelating agents which are expected to extract suitable metal ions from
the environment and thus be subject to accelerated degradation. Many
chelating agents are mentioned, including acetylacetone, acetonyl-acetone,
benzoylacetone, thenoyl trifluoroacetone, trifluoroacetylacetone,
dibenzoylmethane, dipivaloyl methane, n-dodecylacetylacetone,
n-dodecylbenzoylacetone and diethyldithiocarbamate salts.
U.S. Pat. No. 4,121,025 discloses systems in which degradation-promoting
metals are complexed with stabilising organic compounds or groups.
Examples of such metals are Fe, Ag, Pd, Mo, Cr, W and Ce. Examples of the
compounds or groups include tetramethylthiuram disulphide and
bis-dithiocarbamates.
GB-A-1356107 discloses compositions containing Fe, Mn, Ag, Pd, Mo, Cr, W or
Ce with a complexing agent which itself or as a metal complex is an
antioxidant. Dialkyldithiocarbamic acids, iron dialkyldithiocarbamates and
the specific combination of ion dibutyldithiocarbamate and zinc
dibutyldithiocarbamate are described.
GB-A-1586344 discloses compositions containing at least one
photo-activating metal complex (the complexing agent being stabilising)
and at least one light-stabilising complex of Ni, Co or Cu. Examples are
iron dimethyldithiocarbamate with nickeldibutyldithio-carbamate and iron
dibutyldithiocarbamate with cobalt dibutyldithiocarbamate.
GB-A-2187193 discloses compositions containing transition metal complexes
of oxygen ligands and transition or Group II or IV metal complexes of
sulphur ligands, wherein the second complex is less than one-third of the
total complex. Examples are iron acetylacetonate, iron acetylacetonate
with zinc diethyldithiocarbamate, and iron acetylacetonate with nickel
diethyldithiocarbamate. The sulphur complex is for thermal stabilisation.
EP-A-0216412 discloses mixtures of a copper ketonate or diketonate, e.g.
copper acetylacetonate, and a zinc dithiocarbamate, e.g. zinc
dimethyldithiocarbamate.
The known systems are effective but have disadvantages. For example, the
very powerful iron acetylacetonate requires a stabiliser, e.g. zinc
diethyldithiocarbamate, not only to provide an induction period but also
to prevent deterioration of the plastic during initial processing (see
FIG. 1 of GB-A-2187193).
SUMMARY OF THE INVENTION
It has now been found that .beta.-diketones having a cyclic structure are
surprisingly effective constituents of photodegradant systems in polymers
such as polypropylene and polyethylene. Photo-degradant systems containing
the cyclic diketones, themselves or their metal complexes, are stable at
plastics processing temperatures, tend to stabilise the polymer during
processing, and provide an induction period during which the plastic does
not lose its strength or change colour.
The present invention can achieve the desirable object of a pro-degradant
system having an extended induction period, during which there is
substantially no loss of mechanical properties, followed by rapid
degradation to complete breakdown of the polymer.
DESCRIPTION OF THE INVENTION
The polymer that is used in the invention may be any conventional material
of the type used for, say, packaging or protective films. Polyolefins are
preferred, particularly polypropylene and, especially, polyethylene. Low
density polyethylene (LDPE) is the polymer of choice for packaging and
agricultural film.
The amount of the pro-degradant diketone that is used is preferably 0.01 to
5%, more preferably 0.05 to 1%, by weight of the polymer. The diketone is
essentially carbocyclic, i.e. the ring may optionally include heteroatoms
such as O, S or N (optionally substituted), but these or any other
structural components are not inconsistent with the presence of a
--CO--CH.sub.2 --O-- or --CO--CHZ--CO-- group (Z is defined below).
By way of example, the diketone or its complex may have the formula
##STR1##
wherein n is 0, 1, 2 or 3; R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are
independently selected from H, a substituent and optionally-substituted
hydrocarbyl of up to 18 C atoms, any substituents being chosen from
oxo(.dbd.O), NH.sub.2, (di)hydrocarbylamino, acylamino, COOH,
hydrocarbyloxy-carbonyl, CN, halogen and NO.sub.2, or two of R.sup.1,
R.sup.2 and R.sup.3 together with the C atoms to which they are attached,
form an aromatic ring optionally substituted as defined above; and
either m is 1 and Z is H or m is an integer and Z is a metal or an
optionally-substituted hydrocarbyl radical as defined above, having the
valency m. It is also possible that, while the compound remains
essentially carbocyclic, (CR.sup.3 R.sup.4) is replaced by a heteroatom
(including optionally-substituted NH).
If the pro-degradant in the form of a metal complex, the metal may be, for
example, Zn, Cu, Fe, Mn, Ni, Co, Cr or V; the preferred metals are those
that give pale-coloured complexes, e.g. Zn and Mn. n is usually one. One
or more of R.sup.1, R.sup.2, R.sup.3 and R.sup.4 will often be H.
(CR.sup.3 R.sup.4).sub.n is preferably CH.sub.2. Substituents may have up
to 12 C atoms.
In the given formula, m may be one. In this case, examples of suitable
cyclic .beta.-diketones are 1,3-cyclopentanedione, 1,3-cyclohexanedione,
1,3-cycloheptanedione and their substituted homologues in which both
carbonyl groups are capable of tautomerising to enols simultaneously.
Examples of these are dimedone (5,5-dimethyl-1,3-cyclohexanedione) and
5-phenyl-1,3-cyclohexanedione. Cyclic .beta.-diketones where only the
carbonyl group is capable of enolisation are also effective: examples are
1,3-indandione and lawsone. All the above compounds can be converted to
enol ethers and are believed to retain pro-degradant properties, although
their ability to form stable complexes with metals is much reduced.
Alternatively, m is 2 or more: a preferred group of such cyclic
.beta.-diketone derivatives comprises those in which two molecules of
cyclic diketone are linked via an optionally-substituted methylene group,
i.e. Z is --CHR--, R being H or optionally-substituted hydrocarbyl as
defined above. Preferred diketones of this type are MBCD, i.e.
2,2'-methylenebis(1,3-cyclohexanedione), and
2,2'-benzylidenebis(1,3-cyclohexanedione). Such compounds may be formed by
mixing a selected aldehyde (RCHO) with an aqueous or alcoholic solution of
the diketone. In the case of MBCD, the simplest "coupled" derivative,
using formaldehyde, an almost quantitative yield of a water-soluble and
crystalline product can be achieved. The dione used can be either material
isolated from an autoclave product solution (by acidification and
filtration) or the untreated reduction liquor.
Particularly preferred compounds are those where Z is methylene or
substituted methylene, preferred substituents being aryl or naphthyl
optionally substituted by electron-withdrawing groups. The reaction of the
.beta.-diketone with aromatic aldehydes requires an alcoholic or aqueous
medium and more forcing conditions. However, it is not difficult to
prepare colourless crystalline derivatives from aldehydes such as
benzaldehyde and naphthaldehyde in excellent yield.
These double diketone compounds can be used as accelerators of
photo-degradation either as free ketones or as chelates with metals.
Qualitative tests in the laboratory have indicated that substantially
insoluble complexes of 1,3-dione with Fe(II), Fe(III), Mn(II), Cu and Zn
are precipitated when a basic solution of 1,3-dione was reacted with the
corresponding metal salt in aqueous medium.
The free ketones or the metal chelates can be used in combination with
other pro-degradants or anti-degradants to provide systems with desired
combinations of properties. Examples of suitable such other compounds are
the dithiocarbamates disclosed and claimed in EP-A-0165005, e.g. zinc
dialkyldithiocarbamates wherein each alkyl group is a branched-chain
C.sub.5-18 alkyl group, preferably isononyl. Another such other compound
is a thiuram sulphide such as tetrabenzylthiuram disulphide; see
EP-A-0413504 which is also incorporated herein by reference. Any such
additive may be used in a range of amounts as for the diketone
prodegradant.
Thus, for example, the degree of photo-activation imparted to LDPE by MBCD
may be low. At higher concentrations, the additive, like most others, may
exhibit difficulty in permitting the control of induction period and
embrittlement time. It is therefore important to find a suitable class of
compound capable of working synergically with the dione, in order to
enhance photo-activity and give some measure of UV life control along the
lines of that disclosed in GB-A-2187193, using mixed metal
dithiocarbamates. Selection was restricted to essentially colourless
compounds. These included:
(i) hindered phenols which were found to have little, if any, effect on
dione performance;
(ii) benzophenones (light stabilisers) which gave the type of UV life
control looked for but which added nothing to the photo-activity of the
dione; and (iii) white dithiocarbamates: results using ZDNC (the Zn
diisononyl salt) are given below.
The photo-activation of MBCD brought about by ZDNC is surprising, in view
of the relatively poor photo-initiation properties of the metal complexes
of the parent 1,3-cyclohexanedione. A preferred aspect of the invention
lies in a combination of the more active metal complexes of both dione and
dithiocarbamate groups, giving an ultra-fast photodegrading system.
Compositions of the invention may also include other, conventional
ingredients for polymer compositions. For example, a phenolic or other
anti-oxidant may be present, e.g. a hindered phenol of known type, e.g. in
an amount of 0.005 to 5% by wt, with respect to the polymer. Such
anti-oxidants will usually be present if the diketone and any other
compatible materials of the type described above are added to commercial
polymer.
The following Examples illustrate the invention, with reference to the
accompanying drawings.
EXAMPLES 1 TO 11
Unstabilised polypropylene Propathene HF-26 (from the Alkathene range of
polyolefines supplied by I.C.I. Ltd.) was processed in a RAPRA torque
rheometer for 10 minutes at 180.degree. C. with an additive (see Table 1)
at a concentration of 0.1% by wt. The polymer blends were then
compression-moulded at 180.degree. C. to films 0.2 mm (0.008 inch) thick.
Samples of each film were then exposed to UV irradiation in a cabinet and
the progress of photooxidation was monitored by determining carbonyl
formation in the polymer using a Perkin-Elmer 599 IR spectrophotometer.
The time to onset of carbonyl formation is the induction period and the
time to reach a carbonyl index of 0.4 is taken as the embrittlement time.
The results are given in the following Table (in which f =fugitive, i.e.
volatile at processing temperatures).
It can be seen from the Table that the simple cyclic diketones are too
volatile to be used as pro-degradants in their free state. The
2,2'-alkylidene-bis-cyclic diketones in contrast are sufficiently
non-volatile to survive processing operations and also provide an
accelerated or more or less undelayed embrittlement time, while in some
cases providing a usefully long induction period during which the
mechanical properties of the film remain substantially unchanged.
EXAMPLES 12 TO 19
Unstabilised polypropylene was blended, as in Example 1, with 0.1% by wt of
additives comprising complexes of cyclic diketones with various metals.
Induction periods and embrittlement times for films tested as in Example 1
are given in the following Table.
It can be seen from the Table that the metal complexes behave similarly to
the free ligands, which suggests that the structure of the ligand is the
key factor in absorbing radiant energy and then dissipating the energy in
ways that either contribute to the photo-degradation of the base or (as in
the case of Examples 12, 13 and 14) provide partial stabilisation.
______________________________________
Embrittle-
Additive Induction ment
Example
(0.1% w/w) Period (h)
Time (h)
______________________________________
Control
None 10 110
Comp. acetylacetone f f
1 1,3-cyclohexanedione
f f
2 dimedone f f
3 5-phenyl-1,3-cyclo-
f f
hexanedione
4 MBCD 35 105
5 2,2'-methylenebis(5-
0 65
phenyl-1,3-cyclohexane-
dione)
6 2,2'-methylenebis(5,5-
0 65
dimethyl-1,3-cyclohexane-
dione)
7 2,2'-benzylidenebis(1,3-
20 90
cyclohexanedione)
8 2,2'-cinnamylidenebis-
25 90
(1,3-cyclohexanedione)
9 2,2'-naphthylmethylene-
0 60
bis(1,3-cyclohexanedione)
10 2,2'-veratrylidenebis(1,3- 115
cyclohexanedione)
11 2,2'-furfurylidenebis(1,3- 125
cyclohexanedione)
Comp. Iron acetylacetonate
0 90
12 1,3-cyclohexanedione/Zn
90 165
13 1,3-cyclohexanedione/FeIII
60 140
14 1,3-cyclohexanedione/CuII
70 155
15 5-phenyl-1,3-cyclo-
25 75
hexanedione/Zn
16 5-phenyl-1,3-cyclohexane- 85
dione/MnII
17 dimedone/Zn 85
18 MBCD/MnII 105
19 2,2'-methylenebis(5-phenyl- 60
1,3-cyclohexanedione)/MnII
______________________________________
EXAMPLE 20
Screening tests of polypropylene film enabled comparison of bridged and
complexed 1,3-diketone with metal dithiocarbamates. This polymer was
selected because of the relative ease with which it can be photodegraded.
The results of these tests showed that whereas all of the derivatives were
photo-active, the bridged dione (as derived from an aldehyde) has a
similar order of photo-activity to the iron dithiocarbamate and could be
processed with ease at elevated temperature, giving a substantially
odourless melt. Films produced were clear and colourless, with excellent
retained physical properties.
Aromatic bridged diones, e.g. those produced from benzaldehyde and
naphthaldehyde, were measurably more active than MBCD However, in view of
greater difficulty in their synthesis and higher projected manufacturing
costs, MBCD was selected for a more detailed examination, in LDPE.
MBCD was processed in unstabilised Alkathene polymer W.J.G.47 supplied by
I.C.I. Processing at 180.degree. C. was carried out for 10, 20 and 30
minutes, using 0.1% by wt dione concentration. The mixtures, after
quenching, were compression moulded into uniform thickness film of 100
.mu.m. Each film was exposed to standard UV light in a cabinet.
Photo-oxidation progress was monitored by carbonyl determination in the
polymer using a Perkin-Elmer I.R. Spectrophotometer. The loss of additive
through decomposition and/or volatilisation whilst processing at
180.degree. C. is too small to detect over a 10-20 minute period and is
relatively small during the extended 30-minute processing cycle. This
feature is essential for an additive used in such small quantities for a
function of this type.
LDPE films containing (A) 0 or (B) 0.1% by wt MBCD were taken periodically,
during exposure to UV radiation, for determination of tensile strength.
FIG. 1 is a graph of the relationship between tensile strength (S; MPa)
and UV irradiation time (T; hrs) as a measure of the induction period to
carbonyl formation (CO =carbonyl index). Each tensile specimen and each
film was 0.125 mm thick; the processing temperature and time were
180.degree. C. and 10 min.
Mixtures of LDPE with 0.1% by wt MBCD were tested for melt flow index
during an extended mixing cycle at 190.degree. C. using a 2.5 kg load.
There was substantially no change.
The value of these combined measurements is that any interaction between
the additive and the polymer in pro-oxidation or chain cross-linking
results in marked movement in melt flow index: a decrease is indicative of
polymer cross-linking whereas an increase implies chain scission.
A significant fall in tensile strength in polyalkylenes denotes approaching
embrittlement. Both results confirm the solubility and thermal inertness
of this particular addition. They suggest that the diketone tends to
stabilise LDPE in both the melt phase and when initially exposed to UV
light as a film.
The in-depth testing of the dione in LDPE confirmed that this additive had
potentially useful photo-activation properties. In addition, it had
thermal stability, good melt colour with little apparent odour, and
excellent processing properties.
EXAMPLE 21
ZDNC photolytically decomposes when exposed to UV radiation and the
resultant "thiyl" radicals could antagonise otherwise stable molecules.
Initial tests in polypropylene showed a marked degree of synergy between
the two compounds and, as a result, the performance of mixtures was
measured in LDPE.
FIG. 2 is a graph of carbonyl index at 1715 cm.sup.-1 (CO) with respect to
time of UV radiation (T; hrs) in LDPE for (A) 0.05% MBCD +0.05% ZDNC; (B)
0.05% ZDNC; and (C) 0.05% MBCD. The graph shows the remarkable extent to
which the rate of LDPE photo-oxidation is increased as a result of
combining ZDNC with MBCD at a level of 0.05% by wt each. After an
induction period of .about.100 hours, the rate of carbonyl development
(speed of embrittlement) is faster than most other "ultra" systems
examined.
FIG. 3 is a graph analogous to that of FIG. 2, for LDPE +0.05% ZDNC plus
(1) 0.05%, (2) 0.1%, (3) 0.15% or (4) 0.2% of MBCD. The graph of FIG. 4 is
similar, but for a constant amount (0.05%) of MBCD plus (I) 0.05%, (2)
0.1% or (3) (3) 0.15% ZDNC. These graphs show how induction periods can be
altered by, say, a factor of 2-3 when the MBCD concentration is increased.
The contribution to the performance and control of the mixture made by ZDNC
is substantial since it has individual efficiency as a melt flow
stabiliser and thermal antioxidant. Furthermore, mixtures are colourless
and odourless.
EXAMPLE 22
The Mn(II) complex of MBCD was prepared in the laboratory, in near
theoretical yield, from manganese sulphate and MBCD in alkali. The complex
was a fawn-coloured, odourless, amorphous solid.
Various mixtures of MnMBCD and FeDNC (ferric diisononyldithiocarbonate)
were processed with LDPE and compressed into films of standard thickness.
These films were exposed to UV light in the UV cabinet, and the rate of
carbonyl development was measured at intervals. The combination at various
levels provided a wide range of photodegradation rates, in general showing
useful synergism. At equal concentrations of 0.1% by wt of each of MnMBCD
and FeDNC, the oxidation curve showed a maximum synergic effect,
representing the fastest rate of embrittlement of any system tested,
including 0.1% ferric acetylacetonate. Films using the two are coloured
and, as such, their application may be limited to agriculture,
horticulture or trash bags, i.e. possible replacements for the FeDD/NiBuD
combination.
EXAMPLE 23
Mixtures of ZDNC and MBCD (0.1% in total) were added to commercial
polypropylene, i.e. containing 0.1% of a phenolic anti-oxidant. At mixing
ratios of 50:50 and 75:25 (ZDNC:MBCD), a satisfactory relationship between
induction and minimum embrittlement time was achieved.
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